Process for the synthesis of 1-pyridiniumpropane-3-sulphonate

The present invention concerns a new and advantageous synthesis process for preparing 1-pyridiniumpropane-3-sulphonate. 1-pyridinium-3-sulphonate (PPS) is a compound represented by the formula (1): ##STR1##

It is a dipolar ion--or, more commonly called, a zwitterion-widely used in preparing electrolytic baths.

PPS is generally synthesized in two steps. In the first step, one starts from allylalcohol and bisulfite, to obtain propanesultone (2) being used as an intermediate: ##STR2##

In the second step, sultone (2) is caused to react with pyridine to obtain the final product (1): ##STR3##

This synthesis, adopted at present, involves however different drawbacks. To start with--as reported for example by G. E. Milo and E. C. Castro, in Cancer Letters, Vol. 31 (1986), page 1--the propanesultone (2) obtained in the first step is a cancerous substance. Its use is thus subject to a series of precautions and special procedures, such as to make its replacement by less harmful reactants and/or intermediates highly desirable.

A further drawback of the known process lies in the fact that the synthesis--in step Ia--of sultone (2) is technologically very complex, in that it requires a vacuum distillation at a pressure between 127 and 254 pa (1-2 torr), with all the practical problems connected with the creation and maintenance of such a high vacuum.

The object of the present invention is to thus conceive a process for preparing 1-pyridiniumpropane-3-sulphonate, which requires no vacuum steps, which employs no toxic or anyhow harmful intermediates, and which simultaneously allows to obtain high reaction yields.

Said object is reached, with the present invention, by a process for the synthesis of 1-pyridiniumpropane-3-sulphonate, characterized in that said 1-pyridiniumpropane-3-sulphonate is obtained by reacting 1-allylpyridinium chloride and alkaline bisulfite, in an aqueous solution, in the presence of radical initiators.

Said radical initiators are suitably selected from the group consisting of oxygen, hydrogen peroxide, peroxides, alkylhydroperoxides and alkaline or ammonium persulfates.

preferably, the reaction temperature is between 20° C. and the reflux temperature. The reaction is generally carried out with a 1 to 3 mole ratio between the alkaline bisulfite and the 1-allylpyridinium chloride, and the initiator represents 1 to 20% in moles of the 1-allylpiridinium chloride.

The 1-allylpyridinium chloride (3), which acts as precursor for the process of the present invention, can be easily synthesized--as known--in a reaction step previous to the actual process, starting from a mixture of pyridine and allyl chloride, by simple heating between 30 and 100° C.: ##STR4##

According to the invention, the 1-allylpyridinium chloride, however obtained, is dissolved into an aqueous solution and alkaline bisulfite is added thereto. The radical initiator, in catalytic amounts, is then added drop by drop under stirring, while the reaction takes place. If gaseous oxygen or gaseous air are used as initiators, they can be bubbled in the solution for the whole time of the reaction. The pH of the solution is adjusted between 6 and 8, for instance with NaOH. The reaction is carried out, as seen above, at a temperature between 20° C. and the reflux temperature, according to the following scheme: ##STR5##

The PPS obtained through the reaction (IV) can then be isolated in different ways from the mixture of salts formed at the end of the reaction. A specially convenient method, which leads to a particularly pure product, consists in carrying out the selective extraction by means of organic solvents, for instance acetic acid. Use can also be made of mixtures of organic solvents with water. As an alternative, the separation can be carried out using ion exchange resins.

The present invention is now described in further detail, with reference to some non-limiting examples.